I sold a transmission out of my 2000 durango 4.7 4x4. It was working fine. The engine was shot so I am parting it out, but the last it was driven was by me and was on the interstate about 2 months ago. Someone bought the transmission, installed it and now it is not shifting into 3rd and I guess acts crazy when it should shift into 3rd. What could have happened? What are some things that should be checked? It is not throwing any codes. He put new fluid in when he installed it. Thanks.